Telecommunications using a tunable oscillator

ABSTRACT

Systems and techniques are disclosed relating to wireless communications. These systems and techniques involve wireless communications wherein a device may be configured to recover an information signal from a carrier using a reference signal, detect a frequency error in the information signal; and periodically tune the reference signal to reduce the frequency error.

BACKGROUND

1. Field

The present invention relates generally to electronics, and morespecifically, to telecommunications using a tunable oscillator.

2. Background

Consumer demand for mobile wireless services has led to the developmentof an ever increasing number of cellular networks. One such network isbased on code division multiple access (CDMA) technology which supportswireless voice and data services using spread-spectrum communications.In spread-spectrum communications, a large number of signals share thesame frequency spectrum and, as a result, provide a high level of usercapacity. This is achieved by transmitting each signal with a differentpseudo-noise (PN) code that modulates a carrier, and thereby, spreadsthe signal. The transmitted signals are separated in the receiver by acorrelator that uses a corresponding PN code to despread the signal. Theundesired signals, whose codes do not match, are not despread andcontribute only to noise.

A competing network which has become the defacto standard in Europe andAsia is Global System for Mobile Communications (GSM) technology. UnlikeCDMA, GSM uses narrowband time division multiple access (TDMA)technology to support wireless voice and data services. Other popularnetworks that have evolved over the years using TDMA technology includeGeneral Packet Radio Service (GPRS) and EDGE, both which support highspeed data services. These networks may be dispersed throughout thegeographic landscape, each with its own unique set of protocols,services, and data rates.

Today, wireless communication devices are being deployed with technologythat supports multiple cellular networks. Typically, these devices areequipped with a dedicated receiver for each network. A local oscillator(LO) circuit may be used to provide a stable reference signal to eachreceiver. The stable reference signal may be used by each individualreceiver to recover information signals from a high frequency carrier.The LO circuit is typically implemented with a crystal oscillatordriving several frequency multiplier circuits. The frequency multipliercircuits may be individually programmed to provide a reference signal toeach receiver at the proper frequency. In order to maintain goodreceiver performance, a highly accurate and stable crystal oscillator isoften employed. Alternatively, a tunable oscillator, such as a voltagecontrolled temperature compensated crystal oscillator (VCTCXO) may beused. A frequency tracking loop may be used to tune the oscillator tocompensate for manufacturing tolerances, Doppler frequency shifts, anddrift.

In more advanced systems, wireless communication devices may be equippedwith a Global Positioning System (GPS) receiver. GPS is part of asatellite based navigation system developed by the United StatesDepartment of Defense. It provides global coverage with navigationalcapability under various environmental conditions. In a fullyoperational GPS, the entire surface of the earth is covered by up totwenty-four satellites dispersed in six orbits with four satellites ineach orbit. A GPS receiver in the wireless communications device usessignals modulated by a pseudo-random-noise (PRN) code from multiplesatellites to pinpoint its exact location on earth. The raw datagenerated from the GPS receiver may be used for various applications. Byway of example, the raw data may be plugged into map files stored inmemory.

To improve the economic viability of these wireless communicationdevices, the GPS receiver often shares a common LO circuit with thecellular receivers. The problem with this approach is that theperformance of the GPS receiver may be degraded if the crystaloscillator in the LO circuit is being tuned by the frequency trackingloop during GPS operation. Accordingly, there is a need for aninnovative approach that can be used to tune a crystal oscillator in anLO circuit without degrading the performance of the GPS receiver.

SUMMARY

In one aspect of the present invention, a communications device includesa tunable oscillator configured to produce a reference signal, areceiver configured to recover an information signal from a carrierusing the reference signal, and a processor configured to detect afrequency error in the information signal, and periodically tune theoscillator to reduce the frequency error.

In another aspect of the present invention, a communications deviceincludes a tunable oscillator configured to produce a reference signal,a receiver configured to recover an information signal from a carrierusing the reference signal, and a processor configured to detect afrequency error in the information signal, and tune the oscillator ifthe frequency error crosses a threshold.

In yet another aspect of the present invention, a method ofcommunications includes recovering an information signal from a carrierusing a reference signal, detecting a frequency error in the informationsignal, and periodically tuning the reference signal to reduce thefrequency error.

In a further aspect of the present invention, a communications deviceincludes means for producing a reference signal, means for recovering aninformation signal from a carrier using the reference signal, means fordetecting a frequency error in the information signal, and means forperiodically tuning the reference signal to reduce the frequency error.

It is understood that other embodiments of the present invention willbecome readily apparent to those skilled in the art from the followingdetailed description, wherein it is shown and described only severalembodiments of the invention by way of illustration. As will berealized, the invention is capable of other and different embodimentsand its several details are capable of modification in various otherrespects, all without departing from the spirit and scope of the presentinvention. Accordingly, the drawings and detailed description are to beregarded as illustrative in nature and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present invention are illustrated by way of example, andnot by way of limitation, in the accompanying drawings, wherein:

FIG. 1 is a conceptual block diagram illustrating a functional exampleof a receiver system for a wireless communications device;

FIG. 2 is a graphical illustration showing an example of a periodictuning operation for a LO circuit in a wireless communications device;

FIG. 3 is a conceptual block diagram illustrating a functional exampleof a WCDMA processor in a wireless communications device: and

FIG. 4 is a flow diagram illustrating a functional example of theoperation of a threshold detector in a WCDMA processor which may be usedin conjunction with the LO tuning operation.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various embodiments of thepresent invention and is not intended to represent the only embodimentsin which the present invention may be practiced. Each embodimentdescribed in this disclosure is provided merely as an example orillustration of the present invention, and should not necessarily beconstrued as preferred or advantageous over other embodiments. Thedetailed description includes specific details for the purpose ofproviding a thorough understanding of the present invention. However, itwill be apparent to those skilled in the art that the present inventionmay be practiced without these specific details. In some instances,well-known structures and devices are shown in block diagram form inorder to avoid obscuring the concepts of the present invention. Acronymsand other descriptive terminology may be used merely for convenience andclarity and are not intended to limit the scope of the invention. Inaddition, for the purposes of this disclosure, the term “coupled” means“connected to” and such connection can either be direct or, whereappropriate in the context, can be indirect, e.g., through interveningor intermediary devices or other means.

A wireless communications device may be used to access a network orcommunicate with other communication devices through one or morecellular networks. By way of example, the wireless communications devicemay be designed to communicate over a wideband code division multipleaccess (WCDMA) cellular network. Alternatively, the wirelesscommunications device may be designed to communicate over a GSM, GPRS,EDGE, or any other cellular network. In at least one embodiment, thewireless communications device may be designed to operate over multiplecellular networks and have GPS capability. The wireless communicationsdevice, typically referred to as a subscriber station, may be any typeof wireless device that can communicate over a wireless medium with acellular network including, but not limited to, a wireless phone orterminal, a computer, a modem, a personal digital assistant and thelike.

A functional block diagram of a receiver system for a wirelesscommunications device is shown in FIG. 1. The receiver system mayinclude a GPS receiver 102 with an antenna 104. The GPS receiver 102 maybe implemented with a heterodyne architecture with an intermediatefrequency (IF). The receiver system may also include one or morecellular receivers including, by way of example, a WCDMA, GSM, GPRS,EDGE and/or any other cellular receiver. For ease of explanation, thereceiver system is shown with a single direct conversion heterodynecellular receiver 106 designed for WCDMA operation. Those skilled in theart will be readily able to apply the inventive concepts describedthroughout this disclosure to multiple cellular receiver designs. TheWCDMA receiver 106 may share the antenna 104 with the GPS receiver 102,or alternatively, may be equipped with its own. In the embodiment shownin FIG. 1, both the GPS receiver 102 and the WCDMA receiver 106 arecoupled to the same antenna 104 to reduce cost.

A LO circuit 108 may be used to provide a stable reference signal toeach receiver at the appropriate frequency. The LO circuit 108 may beimplemented with a tunable oscillator 110, such as a VCTCXO or othersimilar circuit, coupled to a pair of frequency multiplier circuits 112and 114. The first frequency multiplier circuit 112 may be used togenerate a GPS reference signal 108 a suitable to convert a GPS Dopplercarrier to an IF signal. The second frequency multiplier circuit 114 maybe used to generate a WCDMA reference signal 108 b suitable to convert aWCDMA radio frequency (RF) carrier to a baseband signal. Additionalfrequency multiplier circuits may be used to support additional cellularreceivers that may be present in alternative embodiments of the receiversystem. The voltage applied to the tuning input of the oscillator 110may be biased to compensate for manufacturing tolerances in frequency.

The GPS receiver 102 may include any number of amplifier stages andfilters to increase gain and reduce front end noise of the GPS signalsfrom the antenna 104. The GPS signals may also be downconverted to IFsignals through a mixing operation with the GPS reference signal 108 afrom the LO circuit 108 and sampled to produce a digital basebandsignal. The digital baseband signal may then be code-correlated,demodulated and signal processed to obtain a navigational solution. Thesignal processing function may be performed by a computing algorithmthat is enabled by the user, or alternatively, by the network. When thecomputing algorithm is enabled, the GPS receiver 102 is said to be in an“active” state. Once the GPS receiver 102 obtains the navigationalsolution, it enters an “idle” state until enabled again by the user orthe network.

The function of the WCDMA receiver 106 is to amplify, filter anddownconvert information signals from a WCDMA cellular network for use bya WCDMA processor 116. In a manner similar to the GPS receiver 102, theWCDMA receiver 108 may use any number of amplifier stages and filters toprocess carrier signals from the antenna 104. The information signalsmay be recovered from the carrier through a mixing operation with theWCDMA reference signal 108. The baseband signal from the WCDMA receiver106 may then be provided to the WCDMA processor 116. The WCDMA processor116 may be used to generate demodulated, error-corrected data from theinformation signals. The data may be text, video, audio, or any othertype of data.

The WCDMA processor 116 may be responsible for tuning the LO circuit108. The tuning operation should be done in a way that minimizes theimpact on other receivers. In the embodiment of the receiver systemdescribed thus far, the performance of the GPS receiver 102 may bedegraded during LO tuning, and the WCDMA processor 116 should beimplemented with this in mind. One way to reduce the potential impact onother receivers is to limit the tuning period of the LO circuit 108. Thecriteria for limiting the tuning period may vary depending on thepreferences of the designer, the particular communications applicationand the overall design constraints. In at least one embodiment of theWCDMA processor 116, the LO circuit 108 may be tuned for a shortduration of time at repeated frequency intervals. In another embodimentof the WCDMA processor 116, the LO circuit 108 may be tuned only whenthe frequency error in the baseband signal exceeds a threshold. Thoseskilled in the art will be readily able to determine the criteria mostsuitable to the particular application for controlling the periodictuning of the LO circuit 108.

To illustrate the operation of the WCDMA processor 116, a periodictuning algorithm will be described. For the purposes of this disclosure,the term “periodic” and “periodically” will mean “on occasion” withoutregard to the time period or frequency of the LO tuning operation. Inthe described embodiment, the WCDMA processor 116 may include afrequency tracking function to detect frequency errors in the basebandsignal. The frequency tracking function may be used to compensate thebaseband signal for small frequency errors. For larger frequency errors,a tuning control signal 116 a may be generated by the WCDMA processor116 to tune the LO circuit 108 by adjusting the voltage applied to thetuning input of the oscillator 110. To ensure high performance, thefrequency tracking function should provide baseband signal compensationeven during LO tuning. One or more thresholds may be established in theWCDMA processor 116 and compared against the frequency error todetermine whether the LO circuit 108 should be tuned. These thresholdsmay be different depending on whether the GPS receiver 102 is in theactive or idle state. A state indicator signal 102 a may be providedfrom the GPS receiver 102 to the WCDMA processor 116 to set thethresholds. The thresholds may also be different depending on the typeof cellular receiver. By way of example, the thresholds for a WCDMAreceiver may be different from the thresholds for a GSM receiver. Thoseskilled in the art will be readily able to determine the appropriatethresholds for their particular application based on the overall designconstraints and performance parameters.

In at least one embodiment of the WCDMA processor 116, a first thresholdmay be used to begin the tuning operation of the LO circuit 108. Thefirst threshold may be selected to best accommodate WCDMA operation andmay be adjustable depending upon whether the GPS receiver 102 is in theactive or idle state. To prevent GPS performance degradation during LOtuning, a tuning indicator signal 116 b may be generated by the WCDMAprocessor 116 and provided to the GPS receiver 102 to disable GPSoperation.

Once the tuning operation begins, the WCDMA processor 116 may continuetuning the LO circuit 108 until the frequency error drops below a secondthreshold. Like the first threshold, the second threshold may beselected to best accommodate WCDMA operation and may be adjustabledepending upon whether the GPS receiver 102 is in the active or idlestate. Once the frequency error drops below the second threshold, thetuning operation may be terminated, and the tuning indicator signal 116b may be used to signal the GPS receiver 102 to resume operation.

Before the GPS receiver 102 can resume operation, it must firstreacquire the GPS signal. Acquisition is a coarse synchronizationprocess giving estimates of the PRN code offset and the Doppler carrier.The process involves a two dimensional search through space andfrequency in which a replica code and carrier are aligned with thereceived GPS signal. Multiple frequency hypotheses may be required tocomplete the acquisition process. To reduce the time it takes for signalacquisition, a frequency error signal 116 c generated by the frequencytracking function of the WCDMA processor 116 may be provided to the GPSreceiver 102. This information may be used by the GPS receiver 102 tolimit the search through the frequency spectrum for the Doppler carrier.

The first and second thresholds may be different. The effect of thisapproach is to add an element of hysteresis to the tuning operation ofthe LO circuit 108. This concept will be described with reference toFIG. 2 which plots the LO tuning operation as a function of frequencyerror. Referring to FIG. 2, one can readily see that as the frequencyerror increases from 0 Hz. to the first threshold frequency F₁, the LOtuning operation is not performed. Below the first threshold frequencyF₁, the baseband signal may be compensated in the WCDMA processor forthe frequency error. Should the frequency error, however, cross thefirst threshold frequency F₁, the WCDMA processor 116 begins tuning theLO circuit 108 to reduce the frequency error. The LO tuning operationcontinues until the frequency error drops below the second thresholdfrequency F₂. The separation between the threshold frequencies F₁ and F₂may be optimized by those skilled in the art to minimize the overalltuning duration of the LO circuit 108.

A functional block diagram of a WCDMA processor is shown in FIG. 3. TheWCDMA processor may be implemented with a complex (I-Q) architecture.For ease of explanation, the WCDMA processor 116 will be depictedfunctionally in FIG. 3 without reference to separate I (in-phase) and Q(quadrature) channels. The WCDMA processor 116 includes carrier andtiming recovery circuits feeding a rake receiver 302. The rake receiver302 may use independent fading of resolvable multipaths to achievediversity gain. Specifically, the rake receiver 302 may be configured toprocess one or more multipaths of a downlink transmission to thewireless communications device. Each multipath may be fed into aseparate finger processor to perform PN code despreading and orthogonalvariable spreading factor (OVSF) code decovering. The rake receiver 302may then be used to combine the result from each finger processor torecover the symbols transmitted over the downlink transmission.

The rake receiver output may be used to drive a timing recovery loop304. Timing recovery refers to the process of extracting timinginformation from the downlink transmission and using the timinginformation to synchronize a local clock. This clock (not shown) maythen be used to sample the digital baseband signal from the WCDMAreceiver 106 (see FIG. 1). Specifically, the timing recovery loop 304may be used to estimate the timing error between the symbols recoveredby the RAKE receiver 302 and the local clock rate, and adjust the localclock to minimize the timing error. The local clock (not shown) may thenbe used to control the sampling phase of a decimator 306. Timingrecovery circuits are well known in the art.

The rake receiver output may also be used to drive a frequency trackingloop 308. The frequency tracking loop 308 may be used in conjunctionwith a rotator 310 to compensate for frequency errors in the basebandsignal. The rotator 310 may be implemented with a complex multiplier orother similar device. The frequency error may be computed by any numberof techniques well known in the art.

The frequency error computed by the frequency tracking loop 308 may beprovided to a threshold detector 312. In a manner to be described ingreater detail later, the threshold detector 312 may be used to controlthe periodic tuning of the LO circuit 108 (see FIG. 1). The operation ofthe threshold detector 312 will be described with reference to the flowdiagram of FIG. 4. In step 402, the threshold detector may beinitialized, typically with the application of power. The thresholddetector should remain in the initialization state during signalacquisition. During the initialization state, the threshold detector maybe set to a first state. Although not shown in FIG. 4, should the WCDMAprocessor ever need to reacquire the signal, the threshold detectorshould be forced back into the initialization state.

Once the WCDMA processor acquires the signal, the threshold detector mayexit the initialization state and set the first threshold F₁ in step404. The first threshold F₁ may be adjusted depending on whether the GPSreceiver is in the active or idle state. In step 406, the thresholddetector receives a frequency error measurement F_(e) from the frequencytracking loop and compares it to the first threshold F₁ in step 408. Ifthe measured frequency error F_(e) is less than the first threshold F₁,then the threshold detector loops back to step 406 to await the nextfrequency error measurement F_(e) from the frequency tracking loop. If,on the other hand, the measured frequency error F_(e) exceeds the firstthreshold F₁, then the threshold detector may be set to a second statein step 410.

Once the threshold detector output is set to the second state, thesecond threshold F₂ may be set in step 412. The second threshold F₂ maybe adjusted depending on whether the GPS receiver is in the active oridle state. In step 414, the threshold detector receives a new frequencyerror measurement F_(e) from the frequency tracking loop and compares itto the second threshold F₂ in step 416. If the measured frequency errorF_(e) is greater than the second threshold F₂, then the thresholddetector loops back to step 414 to await the next frequency errormeasurement F_(e) from the frequency tracking loop. If, on the otherhand, the measured frequency error F_(e) drops below the threshold F₂,then the threshold detector output may be set back to the first state instep 418. The threshold detector then loops back to step 404 to awaitthe next frequency error measurement F_(e) from the frequency trackingloop.

Returning to FIG. 3, the threshold detector 312 may be used to control aswitch 314. The switch 314 may be used to demultiplex the frequencyerror computed by the frequency tracking loop 308 onto one of two outputlines depending on the state of the threshold detector 312. When thethreshold detector 312 is in the first state, the frequency error may becoupled to the rotator 310 through the switch 314. In this mode, thefrequency error may be used to compensate the baseband signal withouttuning the LO circuit 108 (see FIG. 1).

The switch 314 may also be configured to couple the frequency error fromthe frequency tracking loop 308 to a converter 318 when the thresholddetector 312 is in the second state. The converter 318 may be used togenerate a pulse width modulated signal corresponding to the frequencyerror. A filter 322 may be used to convert the pulse width modulatedsignal to an analog voltage. The analog voltage is the tuning controlsignal 116 a used to provide coarse tuning of the LO circuit 108 (seeFIG. 1). A scaler 316 may be used to produce a digital signal that canbe applied to the rotator 310 to provide fine tuning in the digitaldomain. To prevent GPS performance degradation, the threshold detector312 may also be used to disable GPS operation through the tuningindicator signal 116 b when the threshold detector 312 is in the secondstate. The frequency error signal 116 c from the frequency tracking loop308 may also be provided to the GPS receiver 102 (see FIG. 1) tofacilitate reacquisition of the GPS signal once the LO circuit 108 (seeFIG. 1) is tuned.

The WCDMA processor may also include a searcher 324 for signalacquisition and synchronization. The acquisition process involves asearch through an unknown region of time and frequency in order to bringa spread spectrum pilot signal into coarse alignment with a replicacode. A PN code generator 326 may be used to sequence through thedifferent PN codes for multiple frequency hypothesis. The searcher 324may also be used to force the threshold detector 312 into the firststate during signal acquisition. With this approach, the signalacquisition process may be performed without tuning the LO circuit 108(see FIG. 1) and disturbing GPS operation. Once the acquisition processis complete, the searcher 324 may use the pilot signal to identifystrong multipath arrivals and assign the fingers in the rake receiver302. The rake receiver 302 uses the fingers as a timing reference tocorrelate the signal for each anticipated multipath reflection.

Those skilled in the art will understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those skilled in the art will further appreciate that the variousillustrative logical blocks, modules, circuits, methods and algorithmsdescribed in connection with the embodiments disclosed herein may beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, circuits,methods and algorithms have been described above generally in terms oftheir functionality. Whether such functionality is implemented ashardware or software depends upon the particular application and designconstraints imposed on the overall system. Skilled artisans mayimplement the described functionality in varying ways for eachparticular application, but such implementation decisions should not beinterpreted as causing a departure from the scope of the presentinvention.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The methods or algorithms described in connection with the embodimentsdisclosed herein may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such that theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anASIC.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

1. A communications device, comprising: a tunable oscillator configuredto produce a reference signal; a receiver configured to recover aninformation signal from a carrier using the reference signal; and aprocessor configured to detect a frequency error in the informationsignal, and periodically tune the oscillator to reduce the frequencyerror.
 2. The communications device of claim 1 wherein the processorfurther comprises a rotator configured to compensate for the frequencyerror concurrently with the periodic tuning of the oscillator.
 3. Thecommunications device of claim 2 wherein the processor is furtherconfigured to operate in a acquisition state and a synchronized state,the processor being further configured to acquire the carrier withouttuning the oscillator during the acquisition state, and periodicallytune the oscillator to reduce the frequency error and use the rotator tocompensate for the frequency error during the synchronized state.
 4. Thecommunications device of claim 1 wherein the tunable oscillator isfurther configured to produce a second reference signal, thecommunications device further comprising a second receiver configured torecover a second information signal from a second carrier using thesecond reference signal, the processor being further configured todisable the second receiver during the tuning of the oscillator.
 5. Thecommunications device of claim 4 wherein the processor is furtherconfigured to provide to the second receiver a signal relating to thefrequency error, and wherein the second receiver is further configuredto use the signal relating to the frequency error to acquire the secondcarrier following the tuning of the oscillator.
 6. The communicationsdevice of claim 4 wherein the second receiver comprises a GlobalPositioning Satellite receiver.
 7. The communications device of claim 6wherein the processor comprises a wide band code division multipleaccess processor.
 8. The communications device of claim 1 wherein theprocessor is further configured to enable the tuning of the oscillatorif the frequency error crosses a first threshold, and once enabled,continue tuning the oscillator until the frequency error is reducedbelow a second threshold.
 9. The communications device of claim 8wherein the first threshold is greater than the second threshold. 10.The communications device of claim 8 wherein the processor is furtherconfigured to interface to a particular communications network, andwherein the first and second thresholds are a function of the particularcommunications network for which the processor is configured tointerface with.
 11. The communications device of claim 8 wherein thetunable oscillator is further configured to produce a second referencesignal, the communications device further comprising a second receiverconfigured to recover a second information signal from a second carrierusing the second reference signal, the second receiver being configuredto operate in an active state and an idle state, and wherein the firstand second thresholds are a function of the state of the secondreceiver.
 12. The communications device of claim 11 wherein the secondreceiver comprises a Global Positioning Satellite receiver, the GlobalPositioning Satellite receiver being in the active state when computinga navigational solution.
 13. A communications device, comprising: atunable oscillator configured to produce a reference signal; a receiverconfigured to recover an information signal from a carrier using thereference signal; and a processor configured to detect a frequency errorin the information signal, and tune the oscillator if the frequencyerror crosses a threshold.
 14. The communications device of claim 13wherein the processor is further configured to tune the oscillator oncethe frequency error crosses the threshold until the frequency error isreduced below a second threshold.
 15. The communications device of claim14 wherein the threshold is greater than the second threshold.
 16. Thecommunications device of claim 13 wherein the processor is furtherconfigured to interface to a particular communications network, andwherein the threshold is a function of the particular communicationsnetwork for which the processor is configured to interface with.
 17. Thecommunications device of claim 13 wherein the tunable oscillator isfurther configured to produce a second reference signal, thecommunications device further comprising a second receiver configured torecover a second information signal from a second carrier using thesecond reference signal, the processor being further configured todisable the second receiver during the tuning of the oscillator.
 18. Thecommunications device of claim 17 wherein the processor is furtherconfigured to provide to the second receiver a signal relating to thefrequency error, and wherein the second receiver is further configuredto use the signal relating to the frequency error to acquire the secondcarrier following the tuning of the oscillator.
 19. The communicationsdevice of claim 17 wherein the second receiver comprises a GlobalPositioning Satellite receiver.
 20. The communications device of claim19 wherein the processor comprises a wide band code division multipleaccess processor.
 21. The communications device of claim 17 wherein thesecond receiver is further configured to operate in an active state andan idle state, and wherein the threshold is a function of the state ofthe second receiver.
 22. The communications device of claim 21 whereinthe second receiver comprises a Global Positioning Satellite receiver,the Global Positioning Satellite receiver being in the active state whencomputing a navigational solution.
 23. A method of communications,comprising: recovering an information signal from a carrier using areference signal; detecting a frequency error in the information signal;and periodically tuning the reference signal to reduce the frequencyerror.
 24. The method of claim 23 further comprising rotating theinformation signal to compensate for the frequency error concurrentlywith the periodic tuning of the reference signal.
 25. The method ofclaim 24 further comprising acquiring the carrier without tuning thereference signal, and wherein the periodic tuning of the referencesignal together with the rotation of the information signal is performedfollowing the carrier acquisition.
 26. The method of claim 23 furthercomprising disabling recovery of a second information signal from asecond carrier using a second reference signal during the tuning of thereference signal, the reference signal and the second reference signalbeing generated from a common oscillator.
 27. The method of claim 26further comprising generating a signal relating to the frequency error,and using the signal to acquire the second carrier following the tuningof the reference signal.
 28. The method of claim 26 wherein the secondcarrier with the second information signal is from a Global PositioningSatellite system.
 29. The method of claim 28 wherein the carrier withthe information signal comprises a wide band code division multipleaccess network.
 30. The method of claim 23 wherein the periodic tuningof the reference signal comprises enabling the tuning of the referencesignal when the frequency error crosses a first threshold, and onceenabled, continuing to tune the reference signal until the frequencyerror is reduced below a second threshold.
 31. The method of claim 30wherein the first threshold is greater than the second threshold. 32.The method of claim 30 further comprising receiving the carrier with theinformation signal from a particular communications network, and whereinthe first and second thresholds are a function of the particularcommunications network from which the carrier is received.
 33. Themethod of claim 30 further comprising periodically computing anavigational solution from a second information signal from a GlobalPositioning Satellite system, the second information signal beingrecovered from a second carrier using a second reference signal, and thereference signal and the second reference signal being generated from acommon oscillator, and wherein the first and second thresholds are afunction of whether the computational solution is being computed.
 34. Acommunications device, comprising: means for producing a referencesignal; means for recovering an information signal from a carrier usingthe reference signal; means for detecting a frequency error in theinformation signal; and means for periodically tuning the referencesignal to reduce the frequency error.
 35. The communications device ofclaim 34 wherein the means for periodically tuning the reference signalis configured to enable the tuning of the reference signal if thefrequency error crosses a first threshold, and once enabled, continuetuning the reference signal until the frequency error is reduced below asecond threshold.
 36. The communications device of claim 34 furthercomprising means for producing a second reference signal, means forrecovering a second information signal from a second carrier using thesecond reference signal, and means for disabling the recovery of thesecond information signal during the tuning of the reference signal, themeans for generating the reference signal and the means for generatingthe second reference signal each comprising a common oscillator.